In the beginning of Collapse OS' Forth version, the readline sub-
system was optional. This is why we had this separate RDLN$ routine
and that the input buffer was allocated at boot time.

It's been a while since the RDLN system has been made mandatory, but
we still paid the complexity tax of this separation. Not anymore.

... and rename it to KEY?. Then, add KEY from KEY? for its blocking
version.

I need this for an upcoming Remote Shell feature. If a Collapse OS
system remotely controls another shell, it needs to be able to poll
both the remote system and the local keyboard at the same time. A
blocking KEY is incompatible with this.

In some places, the polling mechanism doesn't make sense, so this
new KEY? always returns a character. In some places, I just haven't
implemented the mechanism yet, so I kept the old blocking code and
added a "always 1" flag as a temporary shim.

I have probably broken something, but in emulators, Collapse OS runs
fine. It's an important reminder of what will be lost with the new
"dogfooding" approach (see recent mailing list message): without
emulators, it's much harder to to sweeping changes like this without
breaking stuff.

It's fine, I don't expect many more of these core changes to the
system. It's nearly feature-complete.

NetBSD doesn't have ncurses. Linking to curses doesn't seem to change
anything. Tried on OpenBSD and Ubuntu.

With KEY and EMIT being switch words, most of the high layer can
be defined before drivers.

In addition to this change, I've compacted core blocks which were
becoming quite sparse.

De-macroisation negatively impacts speed, but this emulator doesn't
need to be fast. Clear code is more important.

We assume CPU_V20 configuration at all times.

I had forgotten that heads index increment before track index.

Getting a Collapse OS prompt.